Odd if true. It's clearly a universal binary, not sure what's going wrong for you.
reply$ file steam_osx
steam_osx: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]
steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64
steam_osx (for architecture arm64): Mach-O 64-bit executable arm64
This appears to only be in the Steam beta - the version available for download still requires Rosetta. There doesn't seem to be a direct download for the beta - you have to opt into it after installing Steam.
replyNot the OP, but I just downloaded the latest stub from an M2 MacBook Air using Safari and it appears to be an x86_64-only binary:
reply % file /Volumes/Steam/Steam.app/Contents/MacOS/steam_osx
/Volumes/Steam/Steam.app/Contents/MacOS/steam_osx: Mach-O universal binary with 1 architecture: [x86_64:Mach-O 64-bit executable x86_64]
/Volumes/Steam/Steam.app/Contents/MacOS/steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64CMD+I on Steam.app says: "Application (Intel)".
reply% file steam_osx
steam_osx: Mach-O universal binary with 1 architecture: [x86_64:Mach-O 64-bit executable x86_64]
steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64